Semiconductor gas sensors operate by offering a change in electronic conductivity in response to a change in the concentration of a particular gas with which the sensors are in contact. A major challenge for such sensors is that they should be as selective as possible and not alter in resistance when exposed to common interferents such as a change in relative humidity.
A more subtle, although no-less important requirement is that the response that sensors offer to the intended target gas should arise through a single mechanism. In order that the response should be completed as rapidly as possible, it is desirable that the mechanism should operate at the surface of the active element: Bulk changes generally take place more slowly than do surface changes at any particular temperature.
A majority of semiconductor gas sensors produced in the world today employ tin dioxide as the active element, but this material suffers from a number of shortcomings including considerable cross-sensitivity and the need for an initial thermal “soak” in order to improve stability.
Another class of materials, based on the perovskite crystal structure is useful for monitoring oxygen (as shown in granted Patent GB 2,408,333) at high temperature but suffers from the concurrent operation of surface and bulk mechanisms when employed at lower temperature for the detection of reducing gases.
Needs exist for improved sensors, improved semiconductor gas sensors and improved materials for semiconductor gas sensors.